As a liquid crystal display device, display devices using a nematic liquid crystal are prevailing as a mainstream. Display devices according to various methods are in practical use at present, such as a twisted nematic (TN) device having a twist angle of 90°, a super twisted nematic (STN) device having a twist angle of 180° or more, a so-called TFT liquid crystal device using a thin film transistor, a lateral electric field type liquid crystal display device improved in visual angle properties, a vertical alignment type liquid crystal display device, and the like.
As an alignment film for these display devices, industrially, it is general practice to use a film formed by applying a solution of a polyimide precursor, a solvent-soluble polyimide or a mixture of these to form a coating, baking the coating and either carrying out alignment treatment such as rubbing or carrying out no special alignment treatment after the baking.
Properties required for the above liquid crystal alignment film naturally include basic properties such as transparency, heat resistance and chemical resistance, and they also include interfacial properties with a liquid crystal such as a good liquid crystal alignment property and a liquid crystal tilt angle having a stable and proper degree and electric properties such as a voltage retention ratio and a charge accumulation amount when a liquid crystal display device is driven.
Further, from viewpoints of production of a liquid crystal display device, storage stability of a treating agent for liquid crystal alignment, properties of a varnish such as a printing property of the treating agent on a substrate, and properties such as durability against scratches or scraping in the treatment of rubbing a coating film and liability to occurrence and release of electrostatic charges are also important.
Of the above properties, the electrical properties such as the voltage retention ratio and the charge accumulation amount are particularly important for a liquid crystal cell employing an active matrix driving method, such as TFT, and a variety of methods have been proposed. For example, taking it into account that an ether bond in a polyimide structure deteriorates the electrical properties, JP-A-6-228061 proposes a diamino compound having a specific structure free of an ether bond as a raw material for a polyimide. Further, JP-A-8-76128 proposes a method in which a compound having one carboxylic acid anhydride group or tertiary amine group is added to a polyimide-containing polymer.